Reticulated absorbent composite

ABSTRACT

An absorbent composite ( 10 ) having a fibrous matrix that includes absorbent material is disclosed. The fibrous matrix defines voids ( 14 ) and passages between the voids, which are distributed throughout the composite. Absorbent material ( 18 ) is located within some of the voids ( 14 ). Absorbent material located in these voids is expandable into the void. In a preferred embodiment, the composite&#39;s fibrous matrix includes resilient and matrix fibers ( 16 ). The composite optionally includes a wet strength agent.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.09/141,152, filed Aug. 27, 1998, which is a continuation ofInternational application Ser. No. PCT/US98/09682, filed May 12, 1998,which claims the benefit of U.S. Provisional Application No. 60/046,395,filed May 13, 1997, priority of the filing dates of which is herebyclaimed under 35 U.S.C. §§ 120 and 119, respectively. Each of theseapplications is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an absorbent composite and moreparticularly, to a reticulated absorbent composite that includessuperabsorbent material.

BACKGROUND OF THE INVENTION

Cellulose fibers derived from wood pulp are used in a variety ofabsorbent articles, for example, diapers, incontinence products, andfeminine hygiene products. It is desirable for the absorbent articles tohave a high absorbent capacity for liquid as well as to have good dryand wet strength characteristics for durability in use and effectivefluid management. The absorbent capacity of articles made from cellulosefibers is often enhanced by the addition of superabsorbent materials,such as superabsorbent polymers. Superabsorbent polymers known in theart have the capability to absorb liquids in quantities from 5 to 100times or more their weight. Thus, the presence of superabsorbentpolymers greatly increases the liquid holding capacity of absorbentarticles made from cellulose.

Because superabsorbent polymers absorb liquid and swell upon contactwith liquid, superabsorbent polymers have heretofore been incorporatedprimarily in cellulose mats that are produced by the conventional dry,air-laid methods. Wet-laid processes for forming cellulose mats have notbeen used commercially because superabsorbent polymers tend to absorbliquid and swell during formation of the absorbent mats, thus requiringsignificant energy for their complete drying.

Cellulose structures formed by the wet-laid process typically exhibitcertain properties that are superior to those of an air-laid structure.The integrity, fluid distribution, and the wicking characteristics ofwet-laid cellulosic structures are superior to those of air-laidstructures. Attempts to combine the advantages of wet-laid compositeswith the high absorbent capacity of superabsorbent materials has led tothe formation of various wet-laid absorbent composites that includesuperabsorbent materials. Generally, these structures includesuperabsorbent materials distributed as a layer within a multilayeredcomposite. Because the superabsorbent polymer is relatively localizedand not uniformly distributed throughout the absorbent structure andthus renders these composites susceptible to gel blocking. Upon liquidabsorption, superabsorbent materials tend to coalesce and form agelatinous mass that prevents the wicking of liquid to unwetted portionsof the composite. By preventing distribution of acquired liquid from acomposite's unwetted portions, gel blocking precludes the effective andefficient use of superabsorbent materials in fibrous composites. Thediminished capacity of such fibrous composites results from narrowing ofcapillary acquisition and distribution channels that accompaniessuperabsorbent material swelling. The diminution of absorbent capacityand concomitant loss of capillary distribution channels for conventionalabsorbent cores that include superabsorbent material are manifested bydecreased liquid acquisition rates and far from ideal liquiddistribution on successive liquid insults.

Accordingly, there exists a need for an absorbent composite thatincludes superabsorbent material and that effectively acquires and wicksliquid throughout the composite and distributes the acquired liquid toabsorbent material where the liquid is efficiently absorbed and retainedwithout gel blocking. A need also exists for an absorbent composite thatcontinues to acquire and distribute liquid throughout the composite onsuccessive liquid insults. In addition, there exists a need for anabsorbent composition containing superabsorbent materials that exhibitsthe advantages associated with wet-laid composites including wetstrength, absorbent capacity and acquisition, liquid distribution,softness, and resilience. The present invention seeks to fulfill theseneeds and provides further related advantages.

SUMMARY OF THE INVENTION

The present invention relates generally to a reticulated fibrousabsorbent composite containing absorbent material and methods for itsformation. The absorbent composite is a fibrous matrix that includesabsorbent material and has a three-dimensional network of channels orcapillaries. The composite's reticulated nature enhances liquid wicking,acquisition, and distribution, while the absorbent material provideshigh absorbent capacity. Wet strength agents can be incorporated intothe composite to provide wet integrity and also assist in securing theabsorbent material in the composite.

The absorbent composite includes a stable three-dimensional network offibers and channels that afford rapid wicking and acquisition of liquid.The fibers and channels distribute the acquired liquid throughout thecomposite and direct liquid to absorbent material present in thecomposite where the liquid is ultimately absorbed. The compositemaintains its integrity before, during, and after liquid is introduced.In one embodiment, the composite is a densified composite that canrecover its original volume on wetting.

In one aspect, the present invention provides an absorbent compositehaving a fibrous matrix that includes absorbent material. The fibrousmatrix defines voids and passages between the voids, which aredistributed throughout the composite. Absorbent material is locatedwithin some of the voids. The absorbent material located in these voidsis expandable into the void.

In another aspect of the present invention, methods for forming areticulated absorbent composite are provided. In the methods, theabsorbent composite is formed from a wet composite that incorporatesabsorbent material. The method generally includes forming a wetcomposite from a mixture of fibers, absorbent material and, optionally,a wet strength agent in a dispersion medium, and then drying the wetcomposite to provide the composite of the present invention. In oneembodiment of the method, the absorbent material hydrates and swellswhen combined with the dispersion medium in the slurry. Drying the wetcomposite results in dehydration of the swollen absorbent materialaccompanied by decrease in the absorbent material's size. The decreasein size of the swollen absorbent material results in the formation ofvoids in the dried absorbent composite. The voids are connected by anetwork of fibers and channels that provide for liquid acquisition,distribution, and absorption. In one embodiment of the method, thecomposite is formed by a wet-laid method and, in another embodiment, thecomposite is formed by a foam method.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated by reference to thefollowing detailed description, when taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a portion of a reticulated absorbentcomposite formed in accordance with the present invention;

FIG. 2 is a photomicrograph of a cross section of a representativereticulated absorbent composite formed by a wet-laid method inaccordance with the present invention at 12 times magnification;

FIG. 3 is a photomicrograph of the wet-laid composite of FIG. 2 at 40times magnification;

FIG. 4 is a photomicrograph of a cross section of a representativereticulated absorbent composite formed by a foam method in accordancewith the present invention at 12 times magnification,

FIG. 5 is a photomicrograph of the foam-formed composite of FIG. 4 at 40times magnification;

FIG. 6 is a photomicrograph of a cross section of a representativereticulated absorbent composite formed by a wet-laid method inaccordance with the present invention in a wetted state at 8 timesmagnification;

FIG. 7 is a photomicrograph of the wet-laid composite of FIG. 6 at 12times magnification;

FIG. 8 is a photomicrograph of a cross section of a representativereticulated absorbent composite formed by a foam method in accordancewith the present invention in a wetted state at 8 times magnification;

FIG. 9 is a photomicrograph of the foam-formed composite of FIG. 8 at 12times magnification;

FIG. 10 is a cross-sectional view of a portion of an absorbent constructincorporating a reticulated absorbent composite formed in accordancewith the present invention;

FIG. 11 is a cross-sectional view of a portion of another absorbentconstruct incorporating a reticulated absorbent composite formed inaccordance with the present invention;

FIG. 12 is a cross-sectional view of a portion of an absorbent articleincorporating a reticulated absorbent composite formed in accordancewith the present invention;

FIG. 13 is a cross-sectional view of a portion of another absorbentarticle incorporating a reticulated absorbent composite formed inaccordance with the present invention;

FIG. 14 is a cross-sectional view of a portion of another absorbentarticle incorporating a reticulated absorbent composite formed inaccordance with the present invention;

FIG. 15 is a cross-sectional view of a portion of an absorbent constructincorporating a reticulated absorbent composite formed in accordancewith the present invention;

FIG. 16 is a cross-sectional view of a portion of another absorbentconstruct incorporating a reticulated absorbent composite formed inaccordance with the present invention;

FIG. 17 is a cross-sectional view of a portion of another absorbentconstruct incorporating a reticulated absorbent composite formed inaccordance with the present invention;

FIG. 18 is a cross-sectional view of a portion of an absorbent articleincorporating a reticulated absorbent composite formed in accordancewith the present invention;

FIG. 19 is a cross-sectional view of a portion of another absorbentarticle incorporating a reticulated absorbent composite formed inaccordance with the present invention; and

FIG. 20 is a cross-sectional view of a portion of another absorbentarticle incorporating a reticulated absorbent composite formed inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The absorbent composite of the present invention is a reticulatedfibrous composite that includes absorbent material. The absorbentmaterial is distributed substantially throughout the fibrous compositeand serves to absorb and retain liquid acquired by the composite. In apreferred embodiment, the absorbent material is a superabsorbentmaterial. In addition to forming a matrix for the absorbent material,the composite's fibers provide a stable three-dimensional network ofchannels or capillaries that serve to acquire liquid contacting thecomposite and to distribute the acquired liquid to the absorbentmaterial. The composite of the present invention optionally includes awet strength agent that further increases tensile strength andstructural integrity of the composite.

The present composite is a fibrous matrix that includes absorbentmaterial. The fibrous matrix defines voids and passages between thevoids, which are distributed throughout the composite. Absorbentmaterial is located within some of the voids. The absorbent materiallocated in these voids is expandable into the void.

The absorbent composite can be advantageously incorporated into avariety of absorbent articles such as diapers and training pants;feminine care products including sanitary napkins, tampons, and pantliners; adult incontinence products; toweling; surgical and dentalsponges; bandages; food tray pads; and the like.

Because the composite is highly absorbent having a high liquid storagecapacity, the composite can be incorporated into an absorbent article asa liquid storage core. In such a construct, the composite can becombined with one or more other composites or layers including, forexample, an acquisition and/or distribution layer. In one preferredembodiment, the present invention provides an absorbent article, such asa diaper, that includes an acquisition layer overlying a reticulatedstorage core and having a liquid pervious facing sheet and a liquidimpervious backing sheet. Because of the composite's capacity to rapidlyacquire and distribute liquid, the composite can serve as a liquidmanagement layer that acquires and transfers a portion of the acquiredliquid to an underlying storage layer. Thus, in another embodiment, theabsorbent composite can be combined with a storage layer to provide anabsorbent core that is useful in absorbent articles.

The absorbent composite of the present invention is a reticulatedabsorbent composite. As used herein, the term “reticulated” refers tothe composite's open and porous nature characterized as having a stablethree-dimensional network of fibers (i.e., fibrous matrix) that createchannels or capillaries that serve to rapidly acquire and distributeliquid throughout the composite, ultimately delivering acquired liquidto the absorbent material that is distributed throughout the composite.

The reticulated composite of the present invention is an open and stablestructure. The fibrous composite's open and stable structure includes anetwork of capillaries or channels that are effective in acquiring anddistributing liquid throughout the composite. In the composite, fibersform relatively dense bundles that direct fluid throughout the compositeand to absorbent material distributed throughout the composite. Thecomposite's wet strength agent serves to stabilize the fibrous structureby providing interfiber bonding. The interfiber bonding assists inproviding a composite having a stable structure in which the composite'scapillaries or channels remain open before, during, and after liquidinsult. The composite's stable structure provides capillaries thatremain open after initial liquid insult and that are available foracquiring and distributing liquid on subsequent insults.

Referring to FIG. 1, a representative reticulated absorbent composite,indicated generally by reference numeral 10, formed in accordance withthe present invention is a fibrous matrix that includes fibrous regions12 substantially composed of fibers 16 and defining voids 14. Some voidsinclude absorbent material 18. Voids 14 are distributed throughoutcomposite 10.

Representative reticulated composites of the invention are shown inFIGS. 2-9. These composites include 48 percent by weight matrix fibers(i.e., southern pine commercially available from Weyerhaeuser Co. underthe designation NB416), 12 percent by weight resilient fibers (i.e.,polymaleic acid crosslinked fibers), 40 percent by weight absorbentmaterial (i.e., superabsorbent material commercially available fromStockhausen), and about 0.5 percent by weight wet strength agent (i.e.,polyamide-epichlorohydrin resin commercially available from Herculesunder the designation Kymene®). FIG. 2 is a photomicrograph of a crosssection of a representative composite of the invention formed by awet-laid process at 12 times magnification. FIG. 3 is a photomicrographof the same cross section at 40 times magnification. FIG. 4 is aphotomicrograph of a cross section of a representative composite of theinvention formed by a foam process at 12 times magnification. FIG. 5 isa photomicrograph of the same cross section at 40 times magnification.The reticulated nature of the composites is shown in these figures.Referring to FIG. 3, fibrous regions extend throughout the composite,creating a network of channels. Void regions, including those thatinclude absorbent material, appear throughout the composite and are influid communication with the composite's fibrous regions. Absorbentmaterial appears in the composite's voids, generally surrounded by densefiber bundles.

Photomicrographs of the representative composites shown in FIGS. 2-5 ina wetted state are illustrated in FIGS. 6-9, respectively. Thesephotomicrographs were obtained by sectioning freeze-dried compositesthat had acquired synthetic urine under free swell conditions. FIGS. 6and 7 are photomicrographs of the wetted wet-laid composite at 8 timesand 12 times magnification, respectively. FIGS. 8 and 9 arephotomicrographs of the wetted foam-formed composite at 8 times and 12times magnification, respectively. Referring to FIG. 6, absorbentmaterial in the wetted composite has swollen and increased in size tomore fully occupy voids that the absorbent material previously occupiedin the dry composite.

The composite's fibrous matrix is composed primarily of fibers.Generally, fibers are present in the composite in an amount from about20 to about 90 weight percent, preferably from about 50 to about 70weight percent, based on the total weight of the composite. Fiberssuitable for use in the present invention are known to those skilled inthe art and include any fiber from which a wet composite can be formed.

The composite of the invention includes resilient fibers. As usedherein, the term “resilient fiber” refers to a fiber present in thecomposite that imparts reticulation to the composite. Generally,resilient fibers provide the composite with bulk and resiliency. Theincorporation of resilient fibers into the composite allows thecomposite to expand on absorption of liquid without structural integrityloss. Resilient fibers also impart softness to the composite. Inaddition, resilient fibers offer advantages in the composite's formationprocesses. Because of the porous and open structure resulting from wetcomposites that include resilient fibers, these composites drain waterrelatively easily and are therefore dewatered and dried more readilythan wet composites that do not include resilient fibers. Preferably,the composite includes resilient fibers in an amount from about 5 toabout 60 percent by weight, more preferably from about 10 to 40 percentby weight, based on the total weight of the composite.

Resilient fibers include cellulosic and synthetic fibers. Preferredresilient fibers include chemically stiffened fibers, anfractuousfibers, chemithermomechanical pulp (CTMP), and prehydrolyzed kraft pulp(PHKP).

The term “chemically stiffened fiber” refers to a fiber that has beenstiffened by chemical means to increase fiber stiffness under dry andwet conditions. Fibers can be stiffened by the addition of chemicalstiffening agents that can coat and/or impregnate the fibers. Stiffeningagents include the polymeric wet strength agents including resinousagents such as, for example, polyamide-epichlorohydrin andpolyacrylamide resins described below. Fibers can also be stiffened bymodifying fiber structure by, for example, chemical crosslinking.Preferably, the chemically stiffened fibers are intrafiber crosslinkedcellulosic fibers.

Resilient fibers can include noncellulosic fibers including, forexample, synthetic fibers such as polyolefin, polyamide, and polyesterfibers. In a preferred embodiment, the resilient fibers includecrosslinked cellulosic fibers.

As used herein, the term “anfractuous fiber” refers to a cellulosicfiber that has been chemically treated. Anfractuous fibers include, forexample, fibers that have been treated with ammonia.

In addition to resilient fibers, the composite of the invention includesmatrix fibers. As used herein, the term “matrix fiber” refers to a fiberthat is capable of forming hydrogen bonds with other fibers. Matrixfibers are included in the composite to impart strength to thecomposite. Matrix fibers include cellulosic fibers such as wood pulpfibers, highly refined cellulosic fibers, and high surface area fiberssuch as expanded cellulose fibers. Other suitable cellulosic fibersinclude cotton linters, cotton fibers, and hemp fibers, among others.Mixtures of fibers can also be used. Preferably, the composite includesmatrix fibers in an amount from about 10 to about 60 percent by weightand more preferably from about 20 to about 50 percent by weight, basedon the total weight of the composite.

The composite of the present invention preferably includes a combinationof resilient and matrix fibers. In one preferred embodiment, thecomposite includes resilient fibers in an amount from about 5 to about20 percent by weight and matrix fibers in an amount from about 20 toabout 60 percent by weight, based on the total weight of the composite.In a more preferred embodiment, the composite includes from about 10 toabout 15 percent by weight resilient fibers, preferably crosslinkedcellulosic fibers, and from about 40 to about 50 percent by weightmatrix fibers, preferably wood pulp fibers, based on the total weight ofthe composite.

Cellulosic fibers are a basic component of the absorbent composite ofthe present invention. Although available from other sources, cellulosicfibers are derived primarily from wood pulp. Suitable wood pulp fibersfor use with the invention can be obtained from well-known chemicalprocesses such as the kraft and sulfite processes, with or withoutsubsequent bleaching. The pulp fibers may also be processed bythermomechanical, chemithermomechanical methods, or combinationsthereof. The preferred pulp fiber is produced by chemical methods.Ground wood fibers, recycled or secondary wood pulp fibers, and bleachedand unbleached wood pulp fibers can be used. Softwoods and hardwoods canbe used. Details of the selection of wood pulp fibers are well known tothose skilled in the art. These fibers are commercially available from anumber of companies, including Weyerhaeuser Company, the assignee of thepresent invention. For example, suitable cellulose fibers produced fromsouthern pine that are usable with the present invention are availablefrom Weyerhaeuser Company under the designations CF416, NF405, PL416,FR516, and NB416.

The wood pulp fibers of the present invention can also be pretreatedprior to use with the present invention. This pretreatment may includephysical treatment, such as subjecting the fibers to steam, or chemicaltreatment, for example, crosslinking the cellulose fibers using any oneof a variety of crosslinking agents. Crosslinking increases fiber bulkand resiliency, and thereby can improve the fibers' absorbency.Generally, crosslinked fibers are twisted or crimped. The use ofcrosslinked fibers allows the composite to be more resilient, softer,bulkier, have better wicking, and be easier to densify than a compositethat does not include crosslinked fibers. Suitable crosslinked cellulosefibers produced from southern pine are available from WeyerhaeuserCompany under the designation NHB416. Crosslinked cellulose fibers andmethods for their preparation are disclosed in U.S. Pat. Nos. 5,437,418and 5,225,047 issued to Graef et al., expressly incorporated herein byreference.

Intrafiber crosslinked cellulosic fibers are prepared by treatingcellulose fibers with a crosslinking agent. Suitable cellulosecrosslinking agents include aldehyde and urea-based formaldehydeaddition products. See, for example, U.S. Pat. Nos. 3,224,926;3,241,533; 3,932,209; 4,035,147; 3,756,913; 4,689,118; 4,822,453; U.S.Pat. No. 3,440,135, issued to Chung; U.S. Pat. No. 4,935,022, issued toLash et al.; U.S. Pat. No. 4,889,595, issued to Herron et al.; U.S. Pat.No. 3,819,470, issued to Shaw et al.; U.S. Pat. No. 3,658,613, issued toSteijer et al.; and U.S. Pat. No. 4,853,086, issued to Graef et al., allof which are expressly incorporated herein by reference in theirentirety. Cellulose fibers have also been crosslinked by carboxylic acidcrosslinking agents including polycarboxylic acids. U.S. Pat. Nos.5,137,537; 5,183,707; and 5,190,563, describe the use of C₂-C₉polycarboxylic acids that contain at least three carboxyl groups (e.g.,citric acid and oxydisuccinic acid) as crosslinking agents.

Suitable urea-based crosslinking agents include methylolated ureas,methylolated cyclic ureas, methylolated lower alkyl cyclic ureas,methylolated dihydroxy cyclic ureas, dihydroxy cyclic ureas, and loweralkyl substituted cyclic ureas. Specific preferred urea-basedcrosslinking agents include dimethyldihydroxy urea (DMDHU,1,3-dimethyl-4,5-dihydroxy-2-imidazolidinone),dimethylol-dihydroxyethylene urea (DMDHEU,1,3-dihydroxymethyl-4,5-dihydroxy-2-imidazolidinone), dimethylol urea(DMU, bis[N-hydroxymethyl]urea), dihydroxyethylene urea (DHEU,4,5-dihydroxy-2-imidazolidinone), dimethylol-ethylene urea (DMEU,1,3-dihydroxymethyl-2-imidazolidinone), and dimethyl-dihydroxyethyleneurea (DDI, 4,5-dihydroxy-1,3-dimethyl-2-imidazolidinone).

Suitable polycarboxylic acid crosslinking agents include citric acid,tartaric acid, malic acid, succinic acid, glutaric acid, citraconicacid, itaconic acid, tartrate monosuccinic acid, and maleic acid. Otherpolycarboxylic acids crosslinking agents include polymericpolycarboxylic acids such as poly(acrylic acid), poly(methacrylic acid),poly(maleic acid), poly(methylvinylether-co-maleate) copolymer,poly(methylvinylether-co-itaconate) copolymer, copolymers of acrylicacid, and copolymers of maleic acid. The use of polymeric polycarboxylicacid crosslinking agents such as polyacrylic acid polymers, polymaleicacid polymers, copolymers of acrylic acid, and copolymers of maleic acidis described in U.S. patent application Ser. No. 08/989,697, filed Dec.12, 1997, and assigned to Weyerhaeuser Company. Mixtures or blends ofcrosslinking agents can also be used.

The crosslinking agent can include a catalyst to accelerate the bondingreaction between the crosslinking agent and cellulose fiber. Suitablecatalysts include acidic salts, such as ammonium chloride, ammoniumsulfate, aluminum chloride, magnesium chloride, and alkali metal saltsof phosphorous-containing acids.

Although not to be construed as a limitation, examples of pretreatingfibers include the application of surfactants or other liquids thatmodify the surface chemistry of the fibers. Other pretreatments includeincorporation of antimicrobials, pigments, dyes and densification orsoftening agents. Fibers pretreated with other chemicals, such asthermoplastic and thermosetting resins also may be used. Combinations ofpretreatments also may be employed. Similar treatments can also beapplied after the composite formation in post-treatment processes.

Cellulosic fibers treated with particle binders and/ordensification/softness aids known in the art can also be employed inaccordance with the present invention. The particle binders serve toattach other materials, such as cellulosic fiber superabsorbentpolymers, as well as others, to the cellulosic fibers. Cellulosic fiberstreated with suitable particle binders and/or densification/softnessaids and the process for combining them with cellulose fibers aredisclosed in the following U.S. patents and patent applications: (1)U.S. Pat. No. 5,543,215, entitled “Polymeric Binders for BindingParticles to Fibers”; (2) U.S. Pat. No. 5,538,783, entitled“Non-Polymeric Organic Binders for Binding Particles to Fibers”; (3)U.S. Pat. No. 5,300,192, entitled “Wet-laid Fiber Sheet ManufacturingWith Reactivatable Binders for Binding Particles to Binders”; (4) U.S.Pat. No. 5,352,480, entitled “Method for Binding Particles to FibersUsing Reactivatable Binders”; (5) U.S. Pat. No. 5,308,896, entitled“Particle Binders for High-Bulk Fibers”; (6) Ser. No. 07/931,279, filedAug. 17, 1992, entitled “Particle Binders that Enhance FiberDensification”; (7) Ser. No. 08/107,469, filed Aug. 17, 1993, entitled“Particle Binders”; (8) Ser. No. 08/107,219, filed Aug. 17, 1993,entitled “Particle Binding to Fibers”; (9) Ser. No. 08/107,467, filedAug. 17, 1993, entitled “Binders for Binding Water Soluble Particles toFibers”; (10) U.S. Pat. No. 5,547,745, entitled “Particle Binders”; (11)Ser. No. 08/108,218, filed Aug. 17, 1993, entitled “Particle Binding toFibers” and (12) U.S. Pat. No. 5,308,896, entitled “Particle Binders forHigh-Bulk Fibers”; all expressly incorporated herein by reference.

In addition to natural fibers, synthetic fibers including polymericfibers, such as polyolefin, polyamide, polyester, polyvinyl alcohol, andpolyvinyl acetate fibers may also be used in the absorbent composite ofthe present invention. Suitable polyolefin fibers include polyethyleneand polypropylene fibers. Suitable polyester fibers include polyethyleneterephthalate fibers. Other suitable synthetic fibers include, forexample, nylon fibers. The absorbent composite can include combinationsof natural and synthetic fibers.

In one preferred embodiment, the absorbent composite includes acombination of wood pulp fibers (e.g., Weyerhaeuser designation NB416)and crosslinked cellulosic fibers (e.g., Weyerhaeuser designationNHB416). Wood pulp fibers are present in such a combination in an amountfrom about 10 to about 85 weight percent by weight based on the totalweight of fibers.

When incorporated into an absorbent article, the reticulated absorbentcomposite of the present invention can serve as a storage layer foracquired liquids. To effectively retain acquired liquids, the absorbentcomposite includes absorbent material. As used herein, the term“absorbent material” refers to a material that absorbs liquid and thatgenerally has an absorbent capacity greater than the cellulosic fibrouscomponent of the composite. Preferably, the absorbent material is awater-swellable, generally water-insoluble polymeric material capable ofabsorbing at least about 5, desirably about 20, and preferably about 100or more times its weight in saline (e.g., 0.9 percent saline). Theabsorbent material can be swellable in the dispersion medium utilized inthe method for forming the composite. In one embodiment, the absorbentmaterial is untreated and swellable in the dispersion medium. In anotherembodiment, the absorbent material is a coated absorbent material thatis resistant to absorbing water during the composite formation process.

The amount of absorbent material present in the composite can varygreatly depending on the composite's intended use. The amount ofabsorbent material present in an absorbent article, such as an absorbentcore for an infant's diaper, is suitably present in the composite in anamount from about 5 to about 60 weight percent, preferably from about 30to about 50 weight percent, based on the total weight of the composite.

The absorbent material may include natural materials such as agar,pectin, and guar gum, and synthetic materials, such as synthetichydrogel polymers. Synthetic hydrogel polymers include, for example,carboxymethyl cellulose, alkaline metal salts of polyacrylic acid,polyacrylamides, polyvinyl alcohol, ethylene maleic anhydridecopolymers, polyvinyl ethers, hydroxypropyl cellulose, polyvinylmorpholinone, polymers and copolymers of vinyl sulphonic acid,polyacrylates, polyacrylamides, and polyvinyl pyridine among others. Ina preferred embodiment, the absorbent material is a superabsorbentmaterial. As used herein, a “superabsorbent material” refers to apolymeric material that is capable of absorbing large quantities offluid by swelling and forming a hydrated gel (i.e., a hydrogel). Inaddition to absorbing large quantities of fluids, superabsorbentmaterials can also retain significant amounts of bodily fluids undermoderate pressure.

Superabsorbent materials generally fall into three classes: starch graftcopolymers, crosslinked carboxymethylcellulose derivatives, and modifiedhydrophilic polyacrylates. Examples of such absorbent polymers includehydrolyzed starch-acrylonitrile graft copolymers, neutralizedstarch-acrylic acid graft copolymers, saponified acrylic acidester-vinyl acetate copolymers, hydrolyzed acrylonitrile copolymers oracrylamide copolymers, modified crosslinked polyvinyl alcohol,neutralized self-crosslinking polyacrylic acids, crosslinkedpolyacrylate salts, carboxylated cellulose, and neutralized crosslinkedisobutylene-maleic anhydride copolymers.

Superabsorbent materials are available commercially, for example,polyacrylates from Clariant of Portsmouth, Va. These superabsorbentpolymers come in a variety of sizes, morphologies, and absorbentproperties (available from Clariant under trade designations such as IM3500 and IM 3900). Other superabsorbent materials are marketed under thetrademarks SANWET (supplied by Sanyo Kasei Kogyo Kabushiki Kaisha), andSXM477 (supplied by Stockhausen of Greensboro, N.C.). Othersuperabsorbent materials are described in U.S. Pat. No. 4,160,059; U.S.Pat. No. 4,676,784; U.S. Pat. No. 4,673,402; U.S. Pat. No. 5,002,814;U.S. Pat. No. 5,057,166; U.S. Pat. No. 4,102,340; and U.S. Pat. No.4,818,598, all expressly incorporated herein by reference. Products suchas diapers that incorporate superabsorbent materials are described inU.S. Pat. No. 3,699,103 and U.S. Pat. No. 3,670,731.

Suitable superabsorbent materials useful in the absorbent composite ofthe present invention include superabsorbent particles andsuperabsorbent fibers.

In a preferred embodiment, the absorbent composite of the presentinvention includes a superabsorbent material that swells relativelyslowly for the purposes of composite manufacturing and yet swells at anacceptable rate so as not to adversely affect the absorbentcharacteristics of the composite or any construct containing thecomposite. Generally, the smaller the absorbent material, the morerapidly the material absorbs liquid.

The absorbent composite of this invention can optionally include a wetstrength agent. The wet strength agent provides increased strength tothe absorbent composite and enhances the composite's wet integrity. Inaddition to increasing the composite's wet strength, the wet strengthagent can assist in binding the absorbent material, for example,superabsorbent material, in the composite's fibrous matrix.

Suitable wet strength agents include cationic modified starch havingnitrogen-containing groups (e.g., amino groups) such as those availablefrom National Starch and Chemical Corp., Bridgewater, N.J.; latex; wetstrength resins such as polyamide-epichlorohydrin resin (e.g., Kymene®557LX, Hercules, Inc., Wilmington, Del.), polyacrylamide resin(described, for example, in U.S. Pat. No. 3,556,932 issued Jan. 19, 1971to Coscia et al.; also, for example, the commercially availablepolyacrylamide marketed by American Cyanamid Co., Stanford, Conn., underthe trade name Parez™ 631 NC); urea formaldehyde and melamineformaldehyde resins, and polyethylenimine resins. A general discussionon wet strength resins utilized in the paper field, and generallyapplicable in the present invention, can be found in TAPPI monographseries No. 29, “Wet Strength in Paper and Paperboard”, TechnicalAssociation of the Pulp and Paper Industry (New York, 1965).

Generally, the wet strength agent is present in the composition in anamount from about 0.01 to about 2 weight percent, preferably from about0.1 to about 1 weight percent, and more preferably from about 0.3 toabout 0.7 weight percent, based on the total weight of the composite. Ina preferred embodiment, the wet strength agent useful in forming thecomposite of the present invention is a polyamide-epichlorohydrin resincommercially available from Hercules, Inc. under the designationKymene®. The wet and dry tensile strength of an absorbent compositeformed in accordance with the present invention will generally increasewith increasing the amount of wet strength agent. The tensile strengthof a representative composite of this invention is described in Example7.

The absorbent composite of the present invention generally has a basisweight from about 50 to about 1000 g/m², preferably from about 200 toabout 800 g/m². In a more preferred embodiment, the absorbent compositehas a basis weight from about 300 to about 600 g/m². The absorbentcomposite generally has a density from about 0.02 to about 0.7 g/cm³,preferably from about 0.04 to about 0.3 g/cm³. In a more preferredembodiment, the absorbent composite has a density of about 0.15 g/cm³.

In one embodiment, the absorbent composite is a densified composite.Densification methods useful in producing the densified composites ofthe present invention are well known to those in the art. See, forexample, U.S. Pat. No. 5,547,541 and patent application Ser. No.08/859,743, filed May 21, 1997, entitled “Softened Fibers and Methods ofSoftening Fibers,” assigned to Weyerhaeuser Company, both expresslyincorporated herein by reference. Postdryer densified absorbentreticulated storage composites of this invention generally have adensity from about 0.1 to about 0.5 g/cm³, and preferably about 0.15g/cm³. Predryer densification can also be employed. Preferably, theabsorbent composite is densified by either a heated or room temperaturecalender roll method. See, for example, U.S. Pat. Nos. 5,252,275 and5,324,575, both expressly incorporated herein by reference.

The composition of the reticulated absorbent composite of the presentinvention can be varied to suit the needs of the desired end product inwhich it is incorporated. In one preferred embodiment, the absorbentcomposite of the present invention includes about 60 weight percentcellulosic fibers (about 48 percent by weight wood pulp fibers and about12 percent by weight crosslinked cellulosic fibers), about 40 percent byweight absorbent material (e.g., superabsorbent particles), and about0.5 percent by weight wet strength agent (e.g.,polyamide-epichlorohydrin resin, Kymene®, about 10 pounds resin per tonfiber) based on the total weight of the composite.

In another aspect, the present invention provides methods for producinga reticulated absorbent composite. The reticulated absorbent compositeof the present invention can be formed by wet-laid and foam processesknown to those of ordinary skill in the pulp processing art. Arepresentative example of a wet-laid process is described in U.S. Pat.No. 5,300,192, issued Apr. 5, 1994, entitled “Wet-laid Fiber SheetManufacturing with Reactivatable Binders for Binding Particles toFibers”, expressly incorporated herein by reference. Wet-laid processesare also described in standard texts, such as Casey, PULP AND PAPER, 2ndedition, 1960, Volume II, Chapter VIII—Sheet Formation. Representativefoam processes useful in forming the composite of the present inventionare known in the art and include those described in U.S. Pat. Nos.3,716,449; 3,839,142; 3,871,952; 3,937,273; 3,938,782; 3,947,315;4,166,090; 4,257,754; and 5,215,627, assigned to Wiggins Teape andrelated to the formation of fibrous materials from foamed aqueous fibersuspensions, and “The Use of an Aqueous Foam as a Fiber-SuspendingMedium in Quality Papermaking,” Foams, Proceedings of a Symposiumorganized by the Society of Chemical Industry, Colloid and SurfaceChemistry Group, R. J. Akers, Ed., Academic Press, 1976, which describesthe Radfoam process, all expressly incorporated herein by reference.

In the methods of the present invention, the absorbent material isincorporated into the composite during the formation of the composite.Generally, the methods for forming the reticulated absorbent compositeinclude combining the components of the composite in a dispersion medium(e.g., an aqueous medium) to form a slurry and then depositing theslurry onto a foraminous support (e.g., a forming wire) and dewateringto form a wet composite. Drying the wet composite provides thereticulated composite.

As noted above, the reticulated composite of the present invention isprepared from a combination of fibers, absorbent material, andoptionally a wet strength agent in a dispersion medium. In oneembodiment of the method, a slurry is formed by directly combiningfibers, absorbent material, and wet strength agent in a dispersionmedium. In another embodiment, the slurry is prepared by first combiningfibers and the wet strength agent in a dispersion medium to provide afibrous slurry to which is then added absorbent material in a secondstep. In yet another embodiment, a fibrous slurry is combined with asecond slurry containing absorbent material, the combined slurry thenbeing deposited onto the support. Alternatively, individual slurries,for example, a fibrous slurry and a slurry containing absorbentmaterial, can be deposited onto the foraminous support through the useof a divided headbox, for example, a twin slice headbox that depositstwo slurries onto a support simultaneously.

In one embodiment, the slurry or slurries containing the composite'scomponents in a dispersion medium are deposited onto a foraminoussupport. Once deposited onto the support, the dispersion medium beginsto drain from the deposited fibrous slurry. Removal of the dispersionmedium (e.g., dewatering) from the deposited fibrous slurry continuesthrough, for example, the application of heat, pressure, vacuum, andcombinations thereof, and results in the formation of a wet composite.

The reticulated absorbent composite of the present invention isultimately produced by drying the wet composite. Drying removes theremaining dispersion medium and provides an absorbent composite havingthe desired moisture content. Generally, the composite has a moisturecontent less than about 20 percent and preferably has a moisture contentin the range from about 6 to about 10 percent by weight based on thetotal weight of the composite. Suitable composite drying methodsinclude, for example, the use of drying cans, air floats and through airdryers. Other drying methods and apparatus known in the pulp and paperindustry may also be used. Drying temperatures, pressures, and times aretypical for the equipment and methods used, and are known to those ofordinary skill in the art in the pulp and paper industry. Arepresentative wet-laid method for forming a reticulated absorbentcomposite of the invention is described in Example 1.

For foam methods, the fibrous slurry is an aqueous or foam slurry thatfurther includes a surfactant. Suitable surfactants include ionic,nonionic, and amphoteric surfactants known in the art. A representativefoam method for forming a reticulated absorbent composite of theinvention is described in Example 2.

In the methods, the weight percent of the absorbent material in thedeposited slurry will be from about 5 to about 80 percent by weight;fibers will be present in the deposited slurry in an amount from about20 to about 80 percent by weight; and the wet strength agent will bepresent in an amount from about 0.01 to about 2 percent by weight, basedon the total weight of the absorbent material, the fiber, and the wetstrength agent in the slurry. The combined weight of the absorbentmaterial and the fiber in the slurry (i.e., the consistency of theslurry) can range from about 0.05 to about 15 percent by weight based onthe total weight of the absorbent material, fiber, and dispersionmedium.

The deposition of the components of the absorbent composite onto theforaminous support, followed by dewatering, results in the formation ofa wet composite that includes absorbent material that may have absorbedwater and, as a result, swollen in size. The wet composite containingthe water-swollen absorbent material is distributed onto a support fromwhich water (i.e., the dispersion medium) can be withdrawn and the wetcomposite dried. Drying causes the water-swollen absorbent material todehydrate and decrease in size, thereby creating voids in the compositesurrounding the absorbent material.

In the methods of the present invention, the absorbent materialpreferably absorbs less than about 20 times its weight in the dispersionmedium, more preferably less than about 10 times, and even morepreferably less than about 5 times its weight in the dispersion medium.

Foam methods are advantageous for forming the absorbent composite of thepresent invention for several reasons. Generally, foam methods providefibrous webs that possess both relatively low density and relativelyhigh tensile strength. For webs composed of substantially the samecomponents, foam-formed webs generally have densities greater thanair-laid webs and lower than wet-laid webs. Similarly, the tensilestrength of foam-formed webs is substantially greater than for air-laidwebs and approaches the strength of wet-laid webs. Also, the use of foamforming technology allows better control of pore and void size, voidsize to be maximized, the orientation and uniform distribution offibers, and the incorporation of a wide range of materials (e.g., longand synthetic fibers that cannot be readily incorporated into wet-laidprocesses) into the composite.

For fabrication, the reticulated absorbent composite can be formed by afoam process, preferably a process by Ahlstrom Company (Helsinki,Finland). The process encompasses desirable manufacturing efficiencieswhile producing a product with desirable performance characteristics.

The formation of a reticulated absorbent composite of the presentinvention by representative wet-laid and foam processes is described inExamples 1 and 2, respectively. Absorbent properties (i.e., rewet,acquisition time, liquid distribution, dry strength, and resilience) forrepresentative reticulated absorbent composites are described inExamples 3 and 4. Wicking and liquid distribution for a representativeabsorbent composite are described in Examples 5 and 6, respectively. Thetensile strength of representative composites formed in accordance withthe present invention is described in Example 7. The softness (i.e.,Taber stiffness) of representative wet-laid and foam-formed compositesis described in Example 8.

One variable that affects the absorbent composite's performancecharacteristics including, for example, liquid acquisition anddistribution rate and absorbent capacity, is the extent of swelling ofthe absorbent material in the composite. The methods of the presentinvention allow for control and variation of absorbent materialswelling. Absorbent material swelling generally depends on the degree ofcrosslinking (e.g., surface and internal crosslinking) and the amount ofwater absorbed by the absorbent material. The extent of swelling dependson a number of factors including the type of absorbent material, theconcentration of absorbent material in an aqueous environment (e.g., thedispersion medium and the wet composite), and the period of time thatthe absorbent material remains in contact with such an environment.Generally, the lower the concentration of the absorbent material in anaqueous medium and the longer the contact time, the greater the swellingof an absorbent material. Absorbent material swelling can be minimizedby dispensing the absorbent in chilled water.

In general, the greater the initial swelling of the absorbent material,the greater the void volume and, consequently, the lower the density ofthe resulting absorbent composite. The greater the void volume of acomposite, the greater its liquid acquisition rate and, generally, thegreater the composite's absorbent capacity.

As noted above, the composite's voids are formed by the hydration andswelling of absorbent material (i.e., during wet composite formation)and the subsequent dehydration and decrease in size of the absorbentmaterial (i.e., during wet composite drying). Ultimately, the density ofthe composite depends on the extent to which the absorbent materialabsorbs liquid and swells during the formation of the wet composite, andthe conditions and extent to which the wet composite incorporating theswollen absorbent material is dried. Water absorbed by the absorbentmaterial during wet composite formation is removed from the absorbentmaterial, decreasing its size, on drying the wet composite. Thedehydration of the swollen absorbent material defines some of the voidsin the fibrous composite.

The reticulated absorbent composite of the present invention can beincorporated as an absorbent core or storage layer in an absorbentarticle including, for example, a diaper or feminine care product. Theabsorbent composite can be used alone or, as illustrated in FIGS. 10 and11, can be used in combination with one or more other layers. In FIG.10, absorbent composite 10 is employed as a storage layer in combinationwith upper acquisition layer 20. As illustrated in FIG. 11, a thirdlayer 30 (e.g., distribution layer) can also be employed, if desired,with absorbent composite 10 and acquisition layer 20.

A variety of suitable absorbent articles can be produced from theabsorbent composite. The most common include absorptive consumerproducts, such as diapers, feminine hygiene products such as femininenapkins, and adult incontinence products. For example, referring to FIG.12, absorbent article 40 comprises absorbent composite 10 and overlyingacquisition layer 20. A liquid pervious facing sheet 22 overliesacquisition composite 20, and a liquid impervious backing sheet 24underlies absorbent composite 10. The absorbent composite will provideadvantageous liquid absorption performance for use in, for example,diapers. The reticulated structure of the absorbent composite will aidin fluid transport and absorption in multiple wettings. For absorbentarticles that incorporate the composite of the invention and that aresuitable for use as diapers or as incontinence products, the articlescan further include leg gathers.

The construct in FIG. 12 is shown for purposes of exemplifying a typicalabsorbent article, such as a diaper or feminine napkin. One of ordinaryskill will be able to make a variety of different constructs using theconcepts taught herein. For example, a typical construction of an adultincontinence absorbent structure is shown in FIG. 13. The article 50comprises a facing sheet 22, acquisition layer 20, absorbent composite10, and a backing sheet 24. The facing sheet 22 is pervious to liquidwhile the backing sheet 24 is impervious to liquid. In this construct, aliquid pervious tissue 26 composed of a polar, fibrous material ispositioned between absorbent composite 10 and acquisition layer 20.

Referring to FIG. 14, another absorbent article includes a facing sheet22, an acquisition layer 20, an intermediate layer 28, absorbentcomposite 10, and a backing sheet 24. The intermediate layer 28contains, for example, a densified fibrous material such as acombination of cellulose acetate and triacetin, which are combined priorto forming the article. The intermediate layer 28 can thus bond to bothabsorbent composite 10 and acquisition layer 20 to form an absorbentarticle having significantly more integrity than one in which theabsorbent composite and acquisition layer are not bonded to each other.The hydrophilicity of layer 28 can be adjusted in such a way as tocreate a hydrophilicity gradient among layers 10, 28, and 20.

The reticulated absorbent composite of the present invention can also beincorporated as a liquid management layer in an absorbent article suchas a diaper. In such an article, the composite can be used incombination with a storage core or layer. In the combination, the liquidmanagement layer can have a top surface area that is smaller, the samesize, or greater than the top surface area of the storage layer.Representative absorbent constructs that incorporate the reticulatedabsorbent composite in combination with a storage layer are shown inFIG. 15. Referring to FIG. 15, absorbent construct 70 includesreticulated composite 10 and storage layer 72. Storage layer 72 ispreferably a fibrous layer that includes absorbent material. The storagelayer can be formed by any method including air-laid, wet-laid, andfoam-forming methods. The storage layer can be a reticulated compositeof this invention.

An acquisition layer can be combined with the reticulated composite andstorage layer. FIG. 16 illustrates absorbent construct 80 havingacquisition layer 20 overlying composite 10 and storage layer 72.Construct 80 can further include intermediate layer 74 to provideconstruct 90 shown in FIG. 17. Intermediate layer 74 can be, forexample, a tissue layer, a nonwoven layer, an air-laid or wet-laid pad,or a reticulated composite of the invention.

Constructs 70, 80, and 90 can be incorporated into absorbent articles.Generally, absorbent articles 100, 110, and 120, shown in FIGS. 18-20,respectively, include a liquid pervious facing sheet 22, a liquidimpervious backing sheet 24, and constructs 70, 80, and 90,respectively. In such absorbent articles, the facing sheet is joined tothe backing sheet.

The following examples are provided for the purposes of illustration,and not limitation.

EXAMPLES Example 1 Reticulated Absorbent Composite Formation:Representative Wet-laid Method

This example illustrates a wet-laid method for forming a representativeabsorbent composite of the present invention.

A wet-laid composite formed in accordance with the present invention isprepared utilizing standard wet-laid apparatus known to those in theart. A slurry of a mixture of standard wood pulp fibers and crosslinkedpulp fibers (48 and 12 percent by weight, respectively, based on totalweight of dried composite) in water having a consistency of about 0.25to 3 percent is formed. Consistency is defined as the weight percent offibers present in the slurry, based on the total weight of the slurry. Awet strength agent such as Kymene® (0.5 percent based on total compositeweight) is then added to the fibrous mixture. Finally, absorbentmaterial (40 percent by weight based on total weight of dried composite)is added to the slurry, the slurry is thoroughly mixed, and thendistributed onto a wire mesh to form a wet composite. The wet compositeis dried to a moisture content of about 9 to about 15 weight percentbased on total composite weight to form a representative reticulatedabsorbent composite.

Absorbent composites having a variety of basis weights can be preparedfrom the composite formed as described above by pre- or postdryingdensification methods known to those in the art.

Example 2 Reticulated Absorbent Composite Formation: Representative FoamMethod

This example illustrates a foam method for forming a representativeabsorbent composite of the present invention.

A lab-size Waring blender is filled with 4L of water and pulp fibers areadded. The mixture is blended for a short time. Crosslinked cellulosefibers are then added to the pulp fibers and blended for at least oneminute to open the crosslinked fibers and effect mixing of the twofibers. The resulting mixture may contain from 0.07 to 12 percent byweight of solids.

The mixture is placed in a container and blended for a few seconds withan air-entrapping blade. A surfactant (Incronan 30, Croda, Inc.) isadded to the blended mixture. Approximately 1 g active surfactant solidsper gram of fiber is added. The mixture is blended while slowly raisingthe mixer blade height from the rising foam. After about one minute, themixing is terminated, superabsorbent is added, and the mixing isrestarted for another one-half minute at constant mixer blade height.The resulting foam-fiber mixture will have a volume about three timesthe volume of the original mixture.

The mixture is rapidly poured into a sheet mold having an inclineddiffusion plate. After the addition of the mixture, the plate is removedfrom the mold, and a strong vacuum is applied to reduce the foam-fiberheight. After most of the visible foam disappears, the vacuum isdiscontinued and the resulting sheet removed from the mold and passed,along with a forming wire, over a slit couch to remove excess foam andwater.

The sheet is then dried in a drying oven to remove the moisture.

Example 3 Acquisition Times for a Representative Reticulated AbsorbentComposite

In this example, the acquisition time for a representative reticulatedabsorbent composite of the present invention (Composite A) is comparedto a commercially available diaper (Diaper A, Kimberly-Clark).

The tests were conducted on commercially available diapers(Kimberly-Clark) from which the core and surge management layer wereremoved and the surrounds used. The test diapers were prepared byinserting the absorbent composite into the diaper.

The aqueous solution used in the tests is a synthetic urine availablefrom National Scientific under the trade name RICCA. The synthetic urineis a saline solution containing 135 meq./L sodium, 8.6 meq./L calcium,7.7 meq./L magnesium, 1.94% urea by weight (based on total weight), plusother ingredients.

A sample of the absorbent structure was prepared for the test bydetermining the center of the structure's core, measuring 1 inch to thefront for liquid application location, and marking the location with an“X”. Once the sample was prepared, the test was conducted by firstplacing the sample on a plastic base (4¾ inch×19¼ inch) and then placinga funnel acquisition plate (4 inch×4 inch plastic plate) on top of thesample with the plate's hole positioned over the “X”. A donut weight(1400 g) was then placed on top of the funnel acquisition plate to whichwas then attached a funnel (4-inch diameter). Liquid acquisition wasthen determined by pouring 100 mL synthetic urine into the funnel andmeasuring the time from when liquid was first introduced into the funnelto the time that liquid disappeared from the bottom of the funnel intothe sample. The measured time is the acquisition time for the firstliquid insult. After waiting one minute, a second 100 mL portion wasadded to the funnel and the acquisition time for the second insult wasmeasured. After waiting an additional one minute, the acquisition wasrepeated for a third time to provide an acquisition time for the thirdinsult. The acquisition times reported in seconds for each of the threesuccessive 100 mL liquid insults for Diaper A and Composite A aresummarized in Table 1.

TABLE 1 Acquisition Time Comparison Acquisition Time (sec) Insult DiaperA Composite A 1 45 10 2 60 11 3 75 10

As shown in Table 1, liquid is more rapidly acquired by the absorbentcomposite of the invention than for the commercially available diapercontaining an air-laid storage core. The results show that the air-laidcore does not acquire liquid nearly as rapidly as the composite of theinvention. The commercial diaper also exhibited characteristicdiminution of acquisition rate on successive liquid insults. Incontrast, the composite of the invention maintained a relativelyconstant acquisition time as the composite continued to absorb liquid onsuccessive insult. Significantly, the absorbent composite of theinvention exhibits an acquisition time for the third insult that issubstantially less (about fourfold) than that of the commerciallyavailable diaper for initial insult. The results reflect the greaterwicking ability and capillary network for the wet-laid compositecompared to conventional air-laid storage core in general, and theenhanced performance of the reticulated absorbent composite inparticular.

Example 4 Acquisition Rate and Rewet for Representative ReticulatedAbsorbent Composites

In this example, the acquisition time and rewet of representativereticulated absorbent composites of the present invention (designatedComposites A1-A4) are compared to a commercially available diaper(Diaper A, Kimberly-Clark). Composites A1-A4 differ by the method bywhich the composites were dried.

Certain properties of the tested composites including the amount ofsuperabsorbent material (weight percent SAP) in the composite and basisweight for each of the composites are summarized in Table 2.

The tests were conducted on commercially available diapers(Kimberly-Clark) from which the cores were removed and used assurrounds. The test diapers were prepared by inserting the testedcomposites into the diapers.

The acquisition time and rewet are determined in accordance with themultiple-dose rewet test described below.

Briefly, the multiple-dose rewet test measures the amount of syntheticurine released from an absorbent structure after each of three liquidapplications, and the time required for each of the three liquid dosesto wick into the product.

The aqueous solution used in the tests was a synthetic urine availablefrom National Scientific under the trade name RICCA, and as describedabove in Example 1.

A preweighed sample of the absorbent structure was prepared for the testby determining the center of the structure's core, measuring 1 inch tothe front for liquid application location, and marking the location withan “X”. A liquid application funnel (minimum 100 mL capacity, 5-7 mL/sflow rate) was placed 4 inches above the surface of the sample at the“X”. Once the sample was prepared, the test was conducted as follows.The sample was flattened, nonwoven side up, onto a tabletop under theliquid application funnel. The funnel was filled with a dose (100 mL) ofsynthetic urine. A dosing ring ( 5/32 inch stainless steel, 2 inch ID×3inch height) was placed onto the “X” marked on the samples. A first doseof synthetic urine was applied within the dosing ring. Using astopwatch, the liquid acquisition time was recorded in seconds from thetime the funnel valve was opened until the liquid wicked into theproduct from the bottom of the dosing ring. After a twenty-minute waitperiod, rewet was determined. During the twenty minute wait period afterthe first dose was applied, a stack of filter papers (19-22 g, Whatman#3, 11.0 cm or equivalent, that had been exposed to room humidity forminimum of 2 hours before testing) was weighed. The stack of preweighedfilter papers was placed on the center of the wetted area. A cylindricalweight (8.9 cm diameter, 9.8 lb.) was placed on top of these filterpapers. After two minutes the weight was removed, the filter papers wereweighed and the weight change recorded. The procedure was repeated twomore times. A second dose of synthetic urine was added to the diaper,and the acquisition time was determined; filter papers were placed onthe sample for two minutes, and the weight change determined. For thesecond dose, the weight of the dry filter papers was 29-32 g, and forthe third dose, the weight of the filter papers was 39-42 g. The drypapers from the prior dosage were supplemented with additional dryfilter papers.

Liquid acquisition time is reported as the length of time (seconds)necessary for the liquid to be absorbed into the product for each of thethree doses. The results are summarized in Table 2.

Rewet is reported as the amount of liquid (grams) absorbed back into thefilter papers after each liquid dose (i.e., difference between theweight of wet filter papers and the weight of dry filter papers). Theresults are also summarized in Table 2.

TABLE 2 Acquisition Time and Rewet Comparison Acquisition Time Rewet SAPBasis (sec) (g) % Weight Insult Insult Insult Insult Insult InsultComposite (w/w) (gsm) 1 2 3 1 2 3 A1 49.4 568 16 19 26 0.1 0.4 2.4 A238.3 648 17 19 22 0.1 0.7 2.5 A3 35.9 687 29 26 27 0.2 0.2 0.7 A4 38.8672 17 18 21 0.1 0.3 0.9 Commercial 40.0 625 34 35 39 0.1 4.0 12.6air-laid core

As indicated in Table 2, the acquisition times for representativecomposites of the invention (Composites A1-A4) were significantly lessthan for the commercially available core.

The rewet of the representative composites of the invention (CompositesA1-A4) is significantly less than for the other cores. While thecomposites exhibited relatively low rewet initially, after the thirdinsult the commercially available core showed substantial rewet. Incontrast, Composites A continued to exhibit low rewet.

Example 5 Horizontal and Vertical Wicking for a RepresentativeReticulated Absorbent Composite

In this example, the wicking characteristics of a representativereticulated absorbent composite (Composite A) are compared to acommercially available diaper storage core (Diaper B, Procter & Gamble).

The horizontal wicking test measures the time required for liquid tohorizontally wick preselected distances. The test was performed byplacing a sample composite on a horizontal surface with one end incontact with a liquid bath and measuring the time required for liquid towick preselected distances. Briefly, a sample composite strip (40 cm×10cm) was cut from a pulp sheet or other source. If the sheet has amachine direction, the cut was made such that the 40 cm length of thestrip was parallel to the machine direction. Starting at one end of the10 cm width of the strip, a first line was marked at 4.5 cm from thestrip edge and then consecutive lines at 5 cm intervals were markedalong the entire length of the strip (i.e., 0 cm, 5 cm, 10 cm, 15 cm, 20cm, 25 cm, 30 cm, and 35 cm). A horizontal wicking apparatus having acenter trough with level horizontal wings extending away from opposingsides of the trough was prepared. The nonsupported edge of each wing waspositioned to be flush with the inside edge of the trough. On eachwing's end was placed a plastic extension to support each wing in alevel and horizontal position. The trough was then filled with syntheticurine. The sample composite strip was then gently bent at the 4.5 cmmark to form an approximately 45° angle in the strip. The strip was thenplaced on the wing such that the strip lay horizontally and the bent endof the strip extended into and contacted the liquid in the trough.Liquid wicking was timed beginning from when the liquid reached thefirst line marked on the composite 5 cm from the 4.5 cm bend. Thewicking time was then recorded at 5 cm intervals when 50 percent of theliquid front reached the marked interval (e.g., 5 cm, 10 cm). The liquidlevel in the trough was maintained at a relatively constant levelthroughout the test by replenishing with additional synthetic urine. Thehorizontal wicking results are summarized in Table 3.

TABLE 3 Horizontal Wicking Comparison Wicking Time Distance (sec) (cm)Diaper B Composite A 5 48 15 10 150 52 15 290 134 20 458 285 25 783 54030 1703 1117 35 — 1425

The results tabulated above indicate that horizontal wicking is enhancedfor absorbent composite of the invention compared to a conventionalair-laid core. The wicking time for Composite A is about 50 percent ofthat for the conventional diaper core. Thus, the horizontal wicking forComposite A is about 1.5 to about 3 times that of a commerciallyavailable storage core.

The vertical wicking test measures the time required for liquid tovertically wick preslected distances. The test was performed byvertically suspending a sample composite with one end of the compositein contact with a liquid bath and measuring the time required for liquidto wick preselected distances. Prior to the test, sample composites (10cm×22 cm) were cut and marked with consecutive lines 1 cm, 11 cm, 16 cm,and 21 cm from one of the strip's edges. Preferably, samples werepreconditioned for 12 hours at 50 percent relative humidity and 23° C.and then stored in sample bags until testing. The sample composite wasoriented lengthwise vertically and clamped from its top edge at the 1 cmmark allowing its bottom edge to contact a bath containing syntheticurine. Timing was commenced once the strip was contacted with theliquid. The time required for 5 percent of the wicking front to reach 5cm, 10 cm, 15 cm, and 20 cm was then recorded. The vertical wickingresults are summarized in Table 4.

TABLE 4 Vertical Wicking Comparison Wicking Time Distance (sec) (cm)Diaper B Composite A 5 20 6 10 Fell Apart 54 15 — 513 20 — 3780

As for the horizontal wicking results, Composite A had significantlygreater vertical wicking compared to the commercial core. The resultsalso show that the composite of the invention has significantly greaterwet tensile strength compared to the conventional air-laid composite.

Example 6 Liquid Distribution for a Representative Reticulated AbsorbentComposite

In this example, the distribution of liquid in a reticulated absorbentcomposite (Composite A) is compared to that of two commerciallyavailable diapers (Diapers A and B above). The test measures thecapacity of a diaper core to distribute acquired liquid. Perfectdistribution would have 0% deviation from average. Ideal liquiddistribution would result in equal distribution of the applied liquid ineach of the four distribution zones (i.e., about 25% liquid in eachzone).

Liquid distribution is determined by weighing different zones of asample that has been subjected to the multiple-dose rewet test describedabove in Example 4. Basically, after the last rewet, the wings of thediaper are removed and then cut into four equal length distributionzones. Each zone is then weighed to determine the weight of liquidcontained in each zone.

The liquid distribution results for a representative reticulatedabsorbent composite of the invention approaches ideality. The resultsindicate that, while the representative commercial storage coresaccumulate liquid near the site of insult, liquid is efficiently andeffectively distributed throughout the reticulated absorbent storagecore.

Example 7 Wet and Dry Tensile Strength for a Reticulated AbsorbentComposite

In this example, the measurement of wet and dry tensile strength of arepresentative absorbent composite is described.

A dry pad tensile integrity test is performed on a 4 inch by 4 inchsquare test pad by clamping a dry test pad along two opposing sides.About 3 inches of pad length are left visible between the clamps. Thesample is pulled vertically in an Instron testing machine and thetensile strength measured is reported in N/m. The tensile strength isconverted to tensile index, Nm/g, by dividing the tensile strength bythe basis weight g/m².

A wet tensile integrity test is performed by taking a sample compositefrom that which has been immersed in synthetic urine for 10 minutes andthen allowed to drain for 5 minutes and placing the sample in ahorizontal jug. Opposite ends of the sample are clamped and then pulledhorizontally on the Instron testing machine. The wet tensile strength,N/m, is converted to tensile index, Nm/g, by dividing the tensilestrength by the basis weight g/m².

Typically, increasing the amount of Kymene® from 2 to 100 pounds per tonof fiber may increase the dry tensile strength from about 0.15 Nm/g to0.66 Nm/g and the wet tensile strength from about 1.5 Nm/g to about 2.4Nm/g.

Example 8 Taber Stiffness for Representative Reticulated AbsorbentComposites

The stiffness of representative reticulated absorbent composites formedin accordance with the present invention was determined by the Taberstiffness method. Representative composites were formed by wet-laid andfoam methods. These composites included matrix fibers (48 percent byweight, southern pine commercially available from Weyerhaeuser Co. underthe designation NB416), resilient fibers (12 percent by weight,polymaleic acid crosslinked fibers), and absorbent material (40 percentby weight, superabsorbent material commercially available fromStockhausen). One of the wet-laid and one of the foam-formed compositesfurther included a wet strength agent (about 0.5 percent by weight,polyamide-epichlorohydrin resin commercially available from Herculesunder the designation Kymene®.

The stiffness of the foam-formed composites was significantly lower thanthe similarly constituted wet-laid composites. The results also indicatethat, for the wet-laid composites, the inclusion of a wet strength agentincreases the composites' stiffness.

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of this invention.

1. A method for forming an absorbent composite, comprising the steps of:adding superabsorbent particles to a first fibrous slurry comprisingcrosslinked cellulosic fibers in a dispersion medium to form a secondfibrous slurry; depositing the second fibrous slurry on a foraminoussupport to form a wet composite; and drying the wet composite to form anabsorbent composite comprising a fibrous matrix and superabsorbentparticles, wherein the fibrous matrix defines voids and passages betweenvoids distributed substantially throughout the matrix; whereinsuperabsorbent particles are located within some of the voids; andwherein superabsorbent particles located within the voids are expandableinto the voids.
 2. The method of claim 1 wherein the first fibrousslurry further comprises wood pulp fibers.
 3. The method of claim 1wherein the superabsorbent particles are swellable in the dispersionmedium.
 4. The method of claim 1 wherein the superabsorbent particlesabsorb less than about 20 times its weight in the dispersion medium. 5.The method of claim 1 wherein the first fibrous slurry further comprisesa wet strength agent.
 6. The method of claim 5 wherein the wet strengthagent is a polyamide-epichiorohydrin resin.
 7. The method of claim 1wherein the dispersion medium comprises water.
 8. The method of claim 1wherein the dispersion medium further comprises a surfactant.
 9. Themethod of claim 8 wherein the surfactant is selected from the groupconsisting of ionic, nonionic, and amphoteric surfactants.
 10. Themethod of claim 1 wherein the second fibrous slurry has a consistency offrom about 0.05 to about 15 percent solids by weight.
 11. The method ofclaim 1 wherein the method is a wet-laid method.
 12. The method of claim1 wherein the method is a foam method.
 13. The method of claim 1 whereinthe adding superabsorbent particles to crosslinked cellulosic fiberscomprises adding the superabsorbent particles as a chilled watersuspension.
 14. A method for forming an absorbent composite, comprisingthe steps of: combining superabsorbent particles with a dispersionmedium to form an superabsorbent particle slurry; adding thesuperabsorbent particle slurry to a fibrous slurry comprisingcrosslinked cellulosic fibers to provide a fibrous superabsorbentparticle slurry; depositing the fibrous superabsorbent particle slurryon a foraminous support to form a wet composite; and drying the wetcomposite to form an absorbent composite comprising a fibrous matrix andsuperabsorbent particles, wherein the fibrous matrix defines voids andpassages between voids distributed substantially throughout the matrix;wherein superabsorbent particles are located within some of the voids;and wherein the superabsorbent particles located within the voids areexpandable into the voids.
 15. The method of claim 14 wherein the firstfibrous slurry further comprises a wet strength agent.
 16. The method ofclaim 14 wherein the superabsorbent particle slurry comprises chilledwater.